1. Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) device, and more particularly, to a method for dividing a display area to minimize an error between a local dimming block of backlight unit for local dimming and a data analysis area, and an LCD device using the same.
2. Discussion of the Related Art
Recently, flat panel displays have been popular as video displays, such as LCDs, Plasma Display Panels (PDPs), Organic Light Emitting Diodes (OLEDs), etc.
An LCD device includes a liquid crystal panel for displaying an image on a pixel matrix relying on the electrical and optical characteristics of liquid crystals that exhibit anisotropy in dielectric constant and refractive index, a driving circuit for driving the liquid crystal panel, and a backlight unit for irradiating light onto the liquid crystal panel. The gray scale of each pixel is adjusted by controlling the transmittance of light that passes from the backlight unit through the liquid crystal panel and polarizers through changing the orientation of liquid crystals according to a data signal.
In the LCD device, the luminance of each pixel is determined by the product between the luminance of the backlight unit and the light transmittance of liquid crystals that depends on data. The LCD device employs backlight dimming method for the purposes of increasing a contrast ratio and reducing power consumption. The backlight dimming method analyzes input image data and then modulates the image data and adjust a dimming value, for controlling the luminance of the backlight unit, according to the analyzed result. A Light Emitting Diode (LED) backlight unit using LEDs as a light source has recently been used. The LEDs boast of high luminance and low power consumption, compared to conventional lamps. Because the LED backlight unit allow for location-based control, they may be driven by local dimming. According to the local dimming technology, the LED backlight unit is divided into a plurality of light emitting blocks and luminance is controlled on a bock-by-block basis. Local dimming may further increase the contrast ratio and decrease the power consumption since the backlight unit and the liquid crystal panel are divided into a plurality of blocks, local dimming values are decided by analyzing data on a block basis, and data is compensated based on the local dimming values.
Because local dimming is a technique that controls the luminance of backlight unit by analyzing data on a local dimming block basis, an error between a local dimming block of a backlight unit and a data analysis area of a display area brings about a dimming deviation between local dimming blocks. The resulting luminance deviation degrades image quality. To prevent the error between a local dimming block and a data analysis area, a design constraint is imposed that the number of equally divided local dimming blocks should be a factor of “resolution/number of backlight driving ports” so that each local dimming block includes the same number of pixels. However, when a backlight unit is designed in terms of slimming down of the backlight unit or reduction of fabrication cost, it is difficult to satisfy the constraint that the number of local dimming blocks should be a factor of “resolution/number of backlight driving ports”.
Meanwhile, if the number of local dimming blocks is set to be a number other than any factor of “resolution/number of backlight driving ports”, there exist residual pixels that cannot be equally distributed to the local dimming blocks. For example, in an LCD device having a liquid crystal panel with a resolution of 1920 (the number of horizontal pixels)×1080 (the number of vertical pixels) and having a backlight unit that is driven in parallel through four ports, if an LED array is designed with 18 horizontal local dimming blocks, the number of horizontal pixels for a data analysis area corresponding to each local dimming block is “480/18=26.67”. Herein, 480=1920/4. When the number of horizontal pixels for a data analysis area corresponding to each local dimming block is set to an integer, i.e. 26, a data analysis area corresponding to the last local dimming block includes additional 12 residual pixels. Herein, 12=480−(26×18). Therefore, a data analysis area corresponding to each of the first 17 local dimming blocks among the 18 local dimming blocks has 26 horizontal pixels, whereas a data analysis area corresponding to the last 18th local dimming block includes 38 (=26+12) horizontal pixels. An error occurs between a plurality of local dimming blocks and their corresponding data analysis areas as well as between the last local dimming block and its corresponding data analysis area. The resulting luminance deviation caused by a dimming deviation between local dimming blocks degrades image quality.